The present invention relates to a method for fabricating a semiconductor device using copper as an interconnection material.
Higher integration of semiconductor cells and downsizing of chips have accelerated the micronization of the interconnection, and the multi level interconnection. In logic devices having such multi level interconnection, interconnection delay is becoming one dominant factor for signal delay of the devices.
The interconnection delay, which is becoming one factor for the signal delay of the devices has a proportional relationship with a product of an interconnection resistance with an interconnection capacitance. Accordingly, to decrease the interconnection delay it is important to decrease the interconnection resistance and the interconnection capacitance.
As a means for decreasing the interconnection resistance, the use of insulation films of low dielectric constants and the use of Cu as an interconnection material are being studied. Especially the interconnection of Cu, which has low resistibility, is easy to be formed in films, is good in stability and can much contribute to the interconnection delay decrease, is expected to much contribute to higher device performances.
In the step of forming Cu interconnection layers, for the electrical interconnection between the interconnection layers, a contact hole is formed in an insulation film between the interconnection layers by etching. FIG. 14A is a sectional view of a Cu interconnection layer after a contact hole has been formed in. The Cu interconnection layer 104 is buried in an insulation film 102 formed on a substrate 100. A diffusion preventing film 106 and an insulation film 108 are sequentially formed, and the contact hole 110 is formed in the insulation film 108 and the diffusion preventing film 106 down to the Cu interconnection layer 104.
Contaminants 112 of fluorocarbon polymers, etc. produced in the etching stay on the inside wall of the formed contact hole 110. To remove such contaminants 112, wet cleaning using a chemical liquid is usually performed.
In the drying following the wet cleaning, spin drying, which remove a liquid by a centrifugal force generated by the rotation of a substrate, is generally used. The spin drying can sufficiently dry the interior of the contact hole of an about 0.30 μm-diameter formed in the conventional Cu interconnection layer.
However, the diameter of the contact hole is more reduced as the interconnection is more micronized, and when a cleaning liquid enters the contact hole, the capillary phenomena takes place. Accordingly, as the size of the contact hole is more reduced, the spin drying finds it difficult to sufficiently dry the interior of the contact hole.
When the interior of the contact hole is not sufficiently dried, a cleaning liquid or fluorocarbon polymer remaining in the contact hole reacts with H2S and H2O in the atmosphere, and furthermore, the reaction products react with the base Cu interconnection layer. Resultantly, as shown in FIG. 14B, an oxide layer 114 of CuF4, CuO,CuO2, etc. is formed on the surface of the Cu interconnection layer exposed in the contact hole 110 and causes defective contact when the interconnection layers are interconnected.
In the method for fabricating a semiconductor device in which the contact hole is formed before the interconnection layer is patterned, often an alkaline chemical liquid is used for cleaning the contact hole, and a chemical amplification-type resist film 116 is used for patterning the interconnection layer. In this case, when the drying after the cleaning is insufficient, the alkaline chemical liquid remaining in the contact hole even after the drying processing acts on the chemical amplification-type resist as an acid deactivating material. Resultantly, as shown in FIG. 14C, the chemical amplification-type resist film 116 formed on the insulation film 108 has a patterning defect due to the tailing phenomena, and an undesirable condition that the patterning of high precision is difficult will take place.
To overcome defects due to such insufficient drying following the cleaning, various methods have been so far proposed.
For example, Japanese Patent Laid-Open Publication No. Hei8-64514 (1996) discloses a method for low pressure drying following the drying by spin drying. FIG. 15 is the flow chart of the semiconductor fabrication method disclosed in Japanese Patent Laid-Open Publication No. Hei8-64514 (1996). As shown, the step S100 of forming a contact hole by etching is followed sequentially by the step S102 of cleaning with a chemical liquid, the step S104 of drying by spin drying and the step S106 of low pressure drying.
Japanese Patent Laid-Open Publication No. Hei9-275085 (1997) discloses a method of drying by spin drying and low pressure drying and then dry cleaning with plasmas. FIG. 16 is the flow chart of the semiconductor fabrication method disclosed in Japanese Patent Laid-Open Publication No. Hei9-275085 (1997). As shown, the step S200 of forming a contact hole is followed sequentially by the step S202 of leaning with a chemical liquid, the step S204 of drying by spin drying and the step S206 of low pressure drying. Furthermore, the low pressure drying step S206 is followed by the step S208 of dry cleaning with plasmas.
In forming a Cu interconnection layer, a chemical liquid to be used in the cleaning after a contact hole has been formed is generally ammonium fluoride (NH4F) or hydroxyamine (NH2OH). When the surface of the Cu interconnection layer exposed on the bottom of the contact hole is subjected to such alkaline chemical liquid, as shown in FIG. 17, a deteriorated Cu surface layer 118 of CuF4, CuO, Cu2O or others is formed on the surface of the Cu interconnection layer 104. The deteriorated Cu surface layer 118 causes contact resistance increase. Furthermore, the deteriorated Cu surface layer 118 is a cause for defective contact.
However, drying the substrate only by the spin drying or low pressure drying after the chemical liquid cleaning permit the CuF4, CuO and Cu2O produced on the surface of the Cu interconnection layer to remain as they are.
In the method disclosed in the above-described Japanese Patent Laid-Open Publication No. Hei9-275085 (1997), to remove CuF4, CuO and Cu2O formed by the chemical liquid on the surface of the Cu interconnection layer exposed on the bottom of the contact hole, the low pressure drying is followed by the dry cleaning with H2 plasmas. The CuF4, CuO and Cu2O formed on the surface of the Cu interconnection layer are reduced by the plasmas, and then the contact hole is filled with a metal which interconnects the interconnection layers, whereby the occurrence of the contact defect can be suppressed.
However, when an insulation film between the interconnection layers is formed of a low dielectric constant insulation film, such as an organic film, organosilicate film or others, the dry cleaning with H2 plasmas will cause the following disadvantages.
Such low dielectric constant insulation film is etched when exposed to H2 plasmas, and often undesirably has configurational defects, such as bowing, etc. An organic film, for example, is etched as expressed by the following reaction formula and has configurational defects, such as bowing, etc.
 C(s)+4H(g)→Si—*+CH4(g)↑
By being exposed to H2 plasmas, the low dielectric constant insulation film often suffers surface deterioration and changes into a film which easily adsorbs degasified components. That is, as shown in FIG. 18, the insulation film 108 of a low dielectric constant insulation film has a degasified component adsorptive deteriorated film 120 formed on the surface. For example, when the low dielectric constant insulation film is organosilicate film, an adsorption site for degasified components, such as H2O, etc. are formed on the surface of the insulation film 108 as expressed by the following reaction formula.Si—CH3(s)+H(g)→Si—*+CH4(g)↑
To the thus-formed adsorption site for the degasified components, such as H2O, etc., the degasified components, such as H2O, etc. adsorbs as expressed by the following formula.Si—*+H2O→Si—OH2
As described above, when a contact hole is formed in the low dielectric constant insulation film, the dry cleaning using H2 plasmas causes configurational defect and surface deterioration of the low dielectric constant insulation film. Thus, it is considered difficult to provide multi-interconnection layer structures of high stability and reliability.